The correct set of four quantum numbers for the valence electrons of Cesium atom 
(Z = 55) is :
 

 ${ }_{37}Rb:1s^2,2s^{2}2p^6,3s^{2}3p^{6}3d^{10},4s^{2}4p^6,4s^1$   Valence electron is in 5s orbital i.e..,  $5s^1$
 $\therefore n=5,l=0,m=0,S=+\frac{1}{2}or-\frac{1}{2}$